(1) Field of the Invention
This invention relates to improvements in pneumatic percussion hammers.
(2) Prior Art
The specification of my Australian Patent Application No. 81767/87 describes and illustrates a pneumatic percussion hammer having a tubular casing with a top sub to receive air under pressure from the outer tube of a double tube drill stem, and with a bit having an anvil head slidable in a bottom sub of the casing. An axial air feed tube directs air under pressure through the bit and air passages therethrough and a piston slidable on a central air outflow tube is caused to reciprocate by air under pressure directed through an arrangement of air passages and chambers to strike the anvil in a rapid succession of blows which are transmitted to the bit for rock drilling. These hammers have proved to be very successful, and the present invention has been devised with the general object of adding certain improvements which will broaden the versatility and range of applications of the hammer, as well as facilitating its repair and maintenance.